Conventional semiconductor fabrication processes have reduced device geometries in the x, y and z dimensions so as to facilitate the fabrication of relatively dense, complex circuits as a “system on a chip,” or SoC. An example of a SoC is the “multiprocessor” chip, which is composed of multiple processors, various memory technologies for satisfying different data storage requirements, and specialized circuits, all of which are fabricated as an integrated circuit. One type of specialized circuit is a communications port circuit, such as a conventional universal serial bus (“USB”) port circuit. FIG. 1 depicts a functional diagram of a conventional processor-memory system 100 based on a multiprocessor 120 and various memory technologies. Specifically, multiprocessor 120 implements SRAM 101 as internal memory, and dynamic RAM (“DRAM”) 102 and FLASH memory (“FLASH”) 104 as external memories. Typically, DRAM 102 and FLASH 104 are conventional integrated circuit chips (e.g., in separate IC packages) that are soldered or otherwise electrically connected with a circuit board or substrate upon which multiprocessor 120 is mounted and are electrically connected with multiprocessor 120 using electrically conductive traces or the like. Multiprocessor 120 also contains specialized circuits, such as a universal serial bus circuit (“USB circ”) 110 and a gigabit Ethernet circuit (“GEthernet circ”) 112 to establish high-speed communications ports. Typically, each processor (not shown) in multiprocessor 120 corresponds with a dedicated static random access memory (“SRAM”) block in the blocks of SRAM 101, which can operate as quickly as the processor. The SRAM memory blocks are usually designed for a “specific use,” such as storing instructions for execution by a specific processor. A drawback to implementing SRAM 101 in multiprocessor 120 is that conventional SRAM cells are relatively large (e.g., compared to DRAM cells), and, thus, consume relatively large amounts of surface area (e.g., silicon die area).
A common approach to increase memory for multiprocessor 120 adds external DRAM and FLASH memories. DRAM provides relatively high-density RAM memory having a relatively large storage capacity for accommodating applications requiring large amounts of memory. FLASH memory provides long-term (i.e., non-volatile) memory, which neither SRAM 101 nor DRAM memories provide. Typically, DRAM and FLASH memories are used to store data for “general use” by multiple processors. A usual drawback to embedding DRAM and FLASH memory technologies in the same substrate that contains the multiple processors is that they increase the die size, which, in turn, leads to higher product costs. Further, embedding both FLASH and DRAM memory technologies within a single SoC usually requires different fabrication processes, which complicates the manufacturing of multiprocessor 120. To avoid the issues with embedding the various conventional memory technologies with the multiple processors, the DRAM and FLASH memories are implemented respectively as external dynamic RAM (DRAM) 102 and FLASH memory (FLASH) 104. However, at least one drawback of using external DRAM 102 and FLASH 104 is that, when combined with multiprocessor 120, more area is consumed on a printed circuit board, for example, than multiprocessor 120 alone.
There are continuing efforts to improve techniques, systems and devices for implementing memory with multiple processors.
Although the previous drawings depict various examples of the invention, the invention is not limited by the depicted examples. It is to be understood that, in the drawings, like reference numerals designate like structural elements. Also, it is understood that the depictions in the FIGS. are not necessarily to scale.